Nonlinear Optical Switching in a Tin-Based Multilayered Halide Perovskite Activated by Stereoactive Lone Pairs and Confined Rotators.

In recent years, there has been a surge in research enthusiasm on searching for solid-state nonlinear optical (NLO) switching materials in halide perovskites owing to their exceptional structural flexibility, compositional diversity, and broad property tenability. However, the majority of reported halide perovskite NLO switching materials contain toxic elements (e.g., Pb), which raise significant environmental concerns. Herein, we present a novel lead-free multilayered halide perovskite NLO switching material, (BA) 2 (EA) 2 Sn 3 Br 10 ( 1 , where BA is butylammonium and EA is ethylammonium). Driven by the stereochemically active lone-pair electrons of the Sn 2+ cation and the cage-confined effect of EA rotators, 1 undergoes a phase transition with symmetry breaking from P 4/ mnc to Cmc 2 1 , which gives rise to a highly efficient modulation of the quadratic NLO property (0.7 times that of KH 2 PO 4 ) at a high temperature of 353 K. Furthermore, crystallographic investigation combined with theoretical calculations reveals that the efficient modulation of NLO properties in 1 stems from the synergistic effects between stereochemically active lone pair-induced octahedral distortions and order/disorder transformation of organic cations. This study opens up an instructive avenue for designing and advancing environmentally friendly solid-state NLO switches in halide perovskites.